The efficiency and stability of plasma thermal systems for plasma treatment of materials and plasma spraying may be affected by a variety of parameters. Properly establishing a plasma jet and maintaining the operating parameters of the plasma jet may, for example, be influenced by the ability to form a stable arc having a consistent attachment to the electrodes. Similarly, the stability of the arc may also be a function of erosion of the electrodes and/or stability of plasma jet profiling or position. Changes of the profile and position of the plasma jet may result in changes in the characteristics of the plasma jet produced by the plasma torch. Additionally, the quality of a plasma treated material or a coating produced by a plasma system may be affected by such changes of plasma profiling, position and characteristics.
In a conventional twin plasma apparatus 100, as shown in FIG. 1, a cathode and an anode head 10, 20 are generally arranged at approximately a 90 degree angle to one another. A feeding tube 112, generally disposed between the heads, may supply a material to be treated by the plasma. The components are generally arranged to provide a confined processing zone 110 in which coupling of the arcs will occur. The relative close proximity to one another and the small space enclosed thereby, often creates a tendency for the arcs to destabilize, particularly at high voltages and/or at low plasma gas flow rate. The arc destabilization, often termed “side arcing” occurs when the arcs preferentially attach themselves to lower resistance paths. Attempts to prevent side arcing often involve the use of a shroud gases, however, this approach typically results in a more complicated design, as well as lower temperatures and enthalpies of the plasma. The lower plasma temperature and enthalpy consequently result in lower process efficiency.